- introduce zero threshold setting to reset value to 0 below a certain point (resolve#2264)
for example, set pwrPZeroThreshold0 10.0 for active power (or pwrQ... for apparent, pwrModS... for reactive) will reset always reset value to 0, similar to what turned off relay does. Default value is nan, since we can't use 0.0 on account of negative values.
- fix energy magnitude indexes usage, properly reset in API
- simplify sending pwr and emon Visible flags
- allow to use settings prefixes more, remove snsMinDelta & snsMaxDelta and use relative magnitude indexes